1. Field of the Invention
The present invention relates to an arcing horn system to be annexed to an insulator set or the like for supporting an overhead power transmission line.
2. Description of the Related Art
The above mentioned insulator set is described in, for example, Japanese Patent Laid-open Publication Heisei No. 8-321372. In this publication, as shown in FIG. 20, a structure is provided such that a electric line 72 is suspended from a steel tower (not illustrated) through a sequential suspension type insulator set 71 to be supported. In this case, an arcing horn system is constructed in such a manner that a ground side arcing horn 73 as sort of an iron bar and a electric line side arcing horn 74 are disposed as being opposed with each other at the opposite sides interposing the insulator set 71 therebetween. Then, this arcing horn system is disposed at the right and left sides of the insulator set 71. Alternatively, front end sides of the ground side arcing horn 73 and front end sides of the electric line side arcing horn 74 are formed as being inflected downward and upward, respectively.
At each of front end sides of the ground side arcing horn 73, for example, an insulative tube 75 made of a vinyl chloride is disposed. As shown in FIG. 21, this insulative tube 75 is consisted of an inner layer 75a and an outer layer 75b. Then, the insulative tubes 75 are secured to this arcing horn 73 as surrounding the front end sides of the arcing horn 73 and an air vent 76 opening to a lower end face of this insulative tube 75 is formed at the lower part of this arcing horn 73. Alternatively, a middle electrode 77 consisted of a conductive member is embedded in the lower end side of the insulative tubes 75 in a radial direction as facing its inner end to the above mentioned air vent 76. Additionally, a cap 78 covering the above mentioned air vent 76 is attached to the lower end of the insulative tube 75.
On the time of thunder stroke, a flashover path running into the electric line side arcing horn 74 from the front end of the ground side arcing horn 73 via the air vent 76 and the middle electrode 77 is formed. Hence, the insulator set 71 is protected. Further, in this case, the inner surface of the air vent 76 is solved to be damaged by the arc due to thunder stroke, so that cracked gas is generated. Additionally, the air within the insulative tubes 75 is heated by the arc or the like, so that the inner pressure thereof is rapidly increased. As a result, the high pressure gas is injected in jet together with the arc through the air vent 76 and due to a cooling and diffusion behavior or the like of this high pressure gas (hereinafter, referred to as arc jet), for example, it is possible to shutoff the dynamic current of the earth fault at the overhead power transmission line for 77 kV almost in a moment of time.
By the way, the accident current of the above mentioned earth fault is several hundred A (Amperes) while the accident current of the short circuit fault is not less than 1,000 A. With respect to such large amount of electric current, even the above described arcing horn system such that the insulative tubes 75 is disposed at the ground side arcing horn 73 may not be able to shutoff the dynamic current. Therefore, an arcing horn system having a dynamic current shutoff capability upon the short cut fault has been demanded.
Alternatively, the above mentioned cap 78 is blown off by the above mentioned arc jet to drop off. Hence, it is possible to easily confirm whether or not the above described operation is generated after the accident. Then, even if the operation is generated once and the cap 78 drops off, at the subsequent thunder stroke, the outburst of the ark jet is generated substantially in the same way as the above, so that the dynamic current is repeatedly shutoff.
If the above mentioned insulative tube 75 is disposed at the electric line side arcing horn 74, the dynamic current shutoff capability is further improved. Therefore, for example, it is possible to provide an arcing horn system having the enough dynamic current shutoff capability for the short circuit fault in addition to the earth fault upon the thunder stroke. However, in this case, only if the insulative tube 75 as same as the above described one is disposed at the front end of the electric line side arcing horn 74, the above mentioned air vent 76 is opened upward, so that after the cap 78 is dropped off at the first thunder stroke, rain water enters in the air vent 76 and water is apt to remain. Then, if the water remains in the air vent 76 in this way, the flashover property is extremely decreased and it becomes difficult to generate the arc. Therefore, it becomes difficult to obtain the sufficient dynamic current shutoff capability.